This invention relates to a vaporization burner for a heater operated by means of liquid fuel that especially is intended to be used as a vehicle heater or an auxiliary vehicle heater.
On the basis of German Offenlegungschrift No. 32 33 321 and corresponding U.S. Pat. No. 4,530,658, a vaporization burner of the initially mentioned type is known that has an absorbent body projecting into a combusiton chamber of the heater which is supplied with fuel via a fuel feeding device. It has been found that such vaporization burners are sensitive to temperature and to bubbles in the fuel fed via the fuel feeding device. In particular, the service life of such a vaporization burner is reduced by the fact that deposits of coke accumulate, during the operation of the heater, on the absorbent body. The absorbent body is formed, for example, by a fleece, and the coke deposits increase, as a function of time, in a direction toward the area where the fuel enters into the absorbent body. These coke deposits, which spread in a direction toward the fuel entrance, will gradually block the fuel supply so that the heater may break down.
The invention, therefore, has a primary object of overcoming the above-mentioned difficulties and, particularly to provide a vaporization burner of the type mentioned which is not only less sensitive to temperature and bubbles for a better operability of the burner, but especially, also has a longer service life.
According to the invention, a vaporization burner is provided that is advantageous because of the fact that the absorbent body has a first vaporization part for the very volatile fuel components and a second vaporization part for the least volatile fuel components. The fuel feeding device, in this case, leads into the first vaporization part and the second vaporization part faces the combusion chamber of the heater and is separated from the first vaporization part by a material that is impermeable with respect to fuel.
The first vaporization part for the very volatile fuel components, in this case, forms the active part of the vaporization burner, whereas the second vaporization part for the least volatile fuel components forms a passive part of the vaporization burner. When, preferably, the first or active vaporization part is arranged at least partially in the shadow of a glow type ignitor, such as a glow plug, a secure ignition can be ensured and the heat load from the combustion chamber to the active part formed by the first vaporization part is reduced so that a longer service life is obtained. By means of this division of the absorbent body into two parts, provided according to the invention, the sensitivity to temperature and to bubbles of such a vaporization burner is significantly reduced.
Since the least volatile fuel components vaporize at the second vaporization part, erosion phenomena, such as the formation of coke, occurs at the surface of this passive part of the absorbent body but do not impair the function of the active first vaporization part. That is, the erosion and formation of coke are restricted to the second passive vaporization part because the coke is formed by the residues of the less volatile fuel components and it is prevented from spreading to the active vaporization part by the separation that is impermeable with respect to fuel. Furthermore, because the fuel feeding device in the case of the invention leads into the first active vaporization part, a clogging and blocking of the fuel entering area is also effectively prevented so that the operability of the vaporization burner as a whole is maintained longer.
In a further development of the invention, the first vaporization part is smaller in its diameter than the second vaporization part; the axial dimension of the first vaporization part is larger than the axial dimension of the second vaporization part; and the first vaporization part is arranged eccentrically with respect to the center line of the combustion chamber in a direction bringing it closer to glow plug. In the case of such an embodiment of the vaporization burner as the preferred further development according to the invention, a large-volume first vaporization part is obtained having a small area surface that is very active in regard to the vaporization of the very volatile components and which, on the basis of its large absorbing volume, also reduces the sensitivity to bubbles. The passive second vaporization part, on the other hand, has a large area surface that faces the combustion chamber of the heater in order to ensure the operational capability also in the case of erosion (coke formation). Preferably the diameter of the first vaporization part is about half as large as the diameter of the second vaporization part, and the axial dimension of the second vaporization part is about one fourth of the axial dimension of the first vaporization part.
In order to prevent a dripping of the least volatile fuel particles from the outer circumference of the first active vaporization part, and in order to achieve the separation of the first and the second vaporization part at the end of the absorbent body that faces the combustion chamber, the first vaporization part is surrounded by a body that is impermeable with respect to fuel and is preferably developed in the shape of a hollow cylinder approximating the shape of a pipe segment. The part of the fuel containing the least volatile fuel components and that was not vaporized at the active first vaporization part passes along the inside wall of the fuel impermeable body, that faces the first vaporization part, and then over the free end thereof to the second vaporization part, where it can be absorbed and then vaporize.
Advantageously, a body that is impermeable to fuel is also provided at the side of the second vaporization part that faces away from the combustion chamber, said body forming the rear wall of the second vaporization part that faces away from the combustion chamber. This body that is impermeable to fuel, as the rear wall of the second vaporization part, stops the erosion of the second passive vaporization part so that the coke formation and the erosion are restricted to the passive second vaporization part.
Both bodies that are impermeable to fuel may be made of the same material, such as a ceramic material, and in order to simplify manufacturing, these two bodies that are impermeable to fuel may be formed of one piece.
According to another advantageous development of the invention, the first vaporization part is fastened in or at a burner part containing the fuel feeding device, such as a cover closing the combustion chamber, and a single fuel impermeable body carries both the first vaporization part and the second vaporization part. In this case a distance may exist between the burner part at which the first vaporization part is fastened and the second vaporization part in an axial direction, or the fuel-impermeable body forming the rear wall of the second vaporization part extends in an axial direction without any clearance between it and the burner part. In the case of this type of design, the two vaporization parts and the burner part containing the fuel feeding device form a unit that can be handled jointly in order to, for example, make possible a fast exchange of the vaporization burner as a whole.
In order to obtain a surface for the passive second vaporization part that is as large as possible, the second vaporization part has an outside diameter that is slightly smaller than the diameter of the combustion chamber, namely in such a way that it can be inserted into the combustion chamber without difficulty.
Preferably, the two vaporization parts of the absorbent body are formed of layers of fleece which, as a function of the respective existing conditions and requirements, in regard to their characteristics can be mutually adapted to one another.
According to another advantageous design according to the invention, the two fuel-impermeable bodies are constructed in one piece with the cover of the burner and are made, preferably, completely from a ceramic material, thus, simplifying the manufacturing and mounting of the vaporization burner, because assembling work is not required. In order to give the ceramic material of the cover a thickness that is as narrow as possible and in order to, as far as possible, avoid a processing of the ceramic body, the fuel supply connection piece is lead along the outside wall of the cover and is fastened there, for example, by gluing or a similar process. A bore is provided in the cover that leads into the first absorbent body of the vaporization burner and into which the end of the mouth of the fuel supply connection piece is inserted.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.